1. Field of the Invention
The present invention relates generally to optical fiber, and more particularly to coatings for optical fiber and to curable compositions for use in coating optical fiber.
2. Technical Background
Optical fiber has acquired an increasingly important role in the field of telecommunications, frequently replacing existing copper wires. This trend has had a significant impact in all areas of telecommunications, greatly increasing the amount of data that is transmitted. Further increase in the use of optical fiber is foreseen, especially in metro and fiber-to-the-home applications, as local fiber networks are pushed to deliver an ever-increasing volume of audio, video, and data signals to residential and commercial customers. In addition, use of fiber in home and commercial premise networks for internal data, audio, and video communications has begun, and is expected to increase.
Optical fiber is typically made of glass, and usually has a polymeric primary coating and a polymeric secondary coating. The primary coating (also known as an inner primary coating), is typically applied directly to the glass fiber, and when cured forms a soft, elastic, compliant material encapsulating the glass fiber. The primary serves as a buffer to cushion and protect the glass fiber during bending, cabling or spooling. The secondary coating (also known as an outer primary coating) is applied over the primary coating, and functions as a tough, protective outer layer that prevents damage to the glass fiber during processing, handling and use.
The secondary coatings conventionally used in optical fibers are typically crosslinked polymers formed by curing a mixture of an oligomer (e.g. a urethane (meth)acrylate) and at least one monomer (e.g. a (meth)acrylate monomer). Generally, a high Young's modulus is desired in order to provide increased hardness of the protective material. However, an increase in Young's modulus generally serves to increase the brittleness of the material, making it more likely to crack during use. As such, current optical fiber secondary coatings tend to have lower than desirable Young's moduli in order to ensure the necessary robustness.